The present invention relates in general to drive shafts and, in particular, to an improved construction for a drive shaft which reduces manufacturing costs and provides greater latitude in manufacturing techniques.
This invention is especially suitable for use in a scroll compressor wherein a pair of mating scrolls undergo relative orbital movement. In such compressors one scroll is normally held fixed and the other is orbited. A compressible fluid, such as a refrigerant gas, is introduced at the side of the spiral wraps and is compressed as the gas moves under the orbiting motion of the device. The compressed gas is then discharged at the center. By reversing the process, introducing compressed fluid at the center and permitting the fluid expansion to drive the device, a scroll machine can be used as a motor or expander.
Because the orbiting motion of the moving scroll is unbalanced and off axis, a vibrating moment is created which must be appropriately balanced by a suitable counterweight. Current designs for scroll compressors, or other scroll-type rotating machines, require that the counterweight be positioned a considerable axial distance away from the orbiting scroll that the counterweight is intended to counterbalance. Such counterweights are carried by the drive shaft, but fabricating a drive shaft which includes a mounted counterweight by known manufacturing techniques is expensive. Such existing fabrication processes include machining a single cast piece of gray or ductile iron or machining the drive shaft from a forging. Regardless of which of these basic fabrication processes are utilized, the drive shaft must be machined from a single, substantially homogeneous, piece of material thereby requiring substantial manufacturing costs.